When domestic or commercial roof spaces are used as living accommodation, storage or office space, it is preferable that they are at least partially lit by natural light. Sometimes this is achieved by fitting Velux (registered trade mark) or Dormer windows. Although modern Velux and Dormer windows are functional and attractive, planning permission for such structures on a roof is sometimes refused, or they are considered undesirable by the owner of the building. In such circumstances, it is known to provide a skylight comprising a light reflective tube which passes through the roof and projects above the level of the roof. The tube is capped by a light transmissive cover which projects still further above the surface of the roof. The whole assembly is unnecessarily cumbersome and unsightly.